Comments on taxonomy:Historically there has been much confusion between Forster's and common terns. For years S. forsteri in summer plumage was not recognized as a separate species because of the close resemblance. Audubon gave the name of Havell's tern (S. havelli) to this species while in winter plumage. Coues was first to distinguish Havell's tern was actually the winter plumage of Forster's tern *13*. Other names: Havell's tern (Audubon), marsh tern, sea-swallow *03,13*.

Forster's tern occurs in Illinois from late April-mid May, and late July-mid October *01*. This species is a common migrant and occassional summer resident in the NE part of Illinois *01,02*. In 1979 several summered at Lake Calumet and suggested possible nesting activity. The first Illinois nesting record in years was in 1982 at Chain of Lakes State Park where 16 pairs nested producing at least 9 young *22*.

Comments on status:The Forster's tern appeared on the Illinois endangered species list's last revision in 1977. This species apparently depends upon larger inland lakes with marsh borders for nesting and its numbers have probably declined with the loss of this preferred habitat. The Forster's tern still satisfies the 3 requirements for inclusion as an endangered species 1) small population numbers in Illinois, 2) preferred habitat threatened, 3) history of decline *02*. The Forster's tern is also protected under the Migratory Bird Treaty Act, 1918 *19* and the Illinois Wildlife Code. 1971 *24*.

Comments on species-habitat associations:During the breeding season the Forster's tern is strongly associated with marshes, while outside of nesting it is known to frequent beaches and more open water *03,05*. Breeding habitats in Illinois feature fairly large lakes bordered with marshes *02*.

Important plant and animal association: Muskrat lodges, cattails, black terns.Though the Forster's tern nests in marshes it prefers dry nesting sites and is often associated with muskrat houses as a nesting substrate *02*. Cattail stands and detrital cattail mat seem an important factor of breeding habitat *02,04*. Forster's tern comes into contact with black terns during breeding season due to their similar habitat preference, but apparently no competition exists *23*.

Comments on feed-guilding:The Forster's tern eats a more varied diet than other tern spp. Because of its marsh existence it eats more insects than most tern spp., but fish are their principle food item *05,14,15,23*. This species feeds aerially, picks food off surface, and plunges into water after prey *04,05,08,09*. This tern also eats limited amounts of carrion (dead fish and frogs) and bird eggs; sometimes conspecifics *05,11,14*.

Comments on breed-guilding:Forster's terns invariably breed in inland lakes or marshes placing nests near open water but prefers a high, dry substrate (muskrat lodge, piles of vegetation). Exact location of copulation unknown. See *23* for habitat description.

Comments on food habits: General: Because of its breeding habitat the Forster's tern has a more varied diet than the common tern *05,14*. Insects make up a significant proportion of the diet which the Forster's tern may catch on the wing or pick up from the water. Small fishes are their principle food and are caught from the waters surface or by diving into water from a perch or a hover *04,05,13,14,15*. Forster's terns are known to eat dead fish and frogs revealed by receeding ice and also are known to occassionally eat bird eggs *11,14,15,23*.Juvenile: The only mention of juvenile food habits available was of parent terns carrying small fishes in their bills back to nesting areas *10, 11*. It is assumed juveniles adopt adult habits upon fledging and independence *00,09*.Adult: See [FH] general and important food habits.

Comments on environmental associations:General: See species habitat associations.Feeding juvenile: No available information but assume when fledged to utilize feeding.Resting juvenile: No available information but assumed to use nesting area (marsh habitat, tall vegetation) until independent *00*.Feeding adult: Adults are known to feed over open water and in vegetated marshes *04,05,09*. In California it was noted that adults did not fish in their nesting area because it was too limited by vegetation for good fishing and travelled to more open water *11*.Resting adult: No available information but assume rests in and near nest when incubating *00*.Breeding adult: During breeding season the Forster's tern is essentially a bird of marshes *05,15,21*. In Illinois this species is primarily found on marsh bordered lakes slightly larger than those preferred by black terns *02*. For nest sites, higher dry substrates are preferred, i.e. muskrat houses, driftage or matted vegetation *02,21,23*. A stable water level may be important as many nests are lost to flooding *10, 23*. Marshes vegetated with phragmites, typha and scirpus grasses seem to be good habitats *06*.

Physical description: 14-16 1/2 in. length; 30 in. wingspread. Forster's tern is easily mistaken for the common tern, however their calls are very different. In summer it is black-capped with a white breast, light grey mantle. The deeply forked tail is pale grey with white outer edges and a dark border along the inside of fork. Wing tips are silvery white or frost grey. Bill is orange-red with black tip, orange-red feet, and eyes are dark brown. In winter plumage, the head lacks the black cap but is distinguished by narrow black band through and back of the eyes and black spot near ear. The feet are yellowish and bill is dark *03,13,18*.

Reproduction: No information is available for Illinois and little available for other areas. Forster's tern is a migrant species in Illinois and throughout C. U.S. from great lakes to New England. It winters from C. Calif. and Baja, Calif. to S.W. Mexico from E. Mexico north and east along shores of gulf to W. Fla., and from N. Fla. north to Va. Forster's terns arrive approx. late April in Ill., early April in KY, and Minn. in early april *02,05,12*. No information is available on courtship activities but Salt & Willard (1971) reported a "heightened social interaction" from courtship and nesting in San Francisco *09*. Portnoy (1977) reported Forster's terns nested earlier than other terns (early March-July compared to early April- Aug.) in Louisiana *21*. No information is available on choice of territory or nest site. The Forster's tern varies the family custom of nesting by constructing a real nest of vegetation, in rank growths of grass or on drifted mats of sedge *05,13*. Nests vary in construction from a well made structure on an assembled heap of vegetation to a mere hollow in a pile of reeds, muskrat house or muddy or sandy shore. Nests may also be placed in dead reeds or flag being held several feet above water *05,03,13*. Forster's terns may appropriate nests from other birds, i.e. grebes *03*. Construction of the nest remains undescribed. Egg dates: VA, 30 May-12 July (5-28 June); Manitoba, 7 June-12 July (8-21 June); Utah, 5 June-3 July (11-26 June); Calif., 26 May-12 July (27 May-15 June) *05*. Forster's tern usually lays 3-4 (2-5) eggs, 43.0 x 31.0 mm *05,07,13,23*. Eggs may vary from tawny olive to buff having small lavender and grey spots *05,07*. Incubation is apparently done by both sexes and may last from 23-25 days *03,05,06,23*. McNicholl (1983) reports eggs hatch within 1 day of each other in the order laid. Eggs hatched over a 1-5 day period *06*. In San Francisco, many multiple layings were observed and it is assumed that the larger clutches observed are a product of more than 1 female *05*. Forster's tern is known to raise only 1 brood per year *05,13,14*. Upon hatching young are downy, clay colored to buff and heavily streaked or spotted with black *05*. Chicks hatch with eyes open but remain in nest for first day or 2 *03,05*. Young are fed by parents until fully grown and able to fly after which they are recruited into the hunting population *05,06*. Flight age is unknown.

Behavior: No information is available on territoriality or home range. Forster's terns are known to nest in loose colonies or solitarily *03*. Bent (1921) describes one colony as having 12 nests in 30 yds. square *05*. Scharf (1979) noted 35-40 pair on .012 ha *04*. Outside of nesting season Forster's tern frequents bays, beaches and oceans, but during breeding season prefers marsh habitat (i.e. phragmites, Typha and Scirpus spp.). Van Rossen (1933) reported this species traveling 2 miles to feeding areas *11*. This particular colony never fed in their nesting area for it was too limited by vegetation for good fishing. The Forster's tern may prefer open water for fishing. Salt & Willard (1971) reported this species fishing with a specialized mode of flying over water and diving which made it able to capitalize on the small fishes which live in shallow waters or in upper levels of larger bodies of water *09*. The Forster's tern is radically hostile to other bird species but sociable to its own kind (except during breeding season) *05*. A strong suggestion of nesting may be the attack behavior of the parents *22*.

Limiting factors: Probably, the most limiting factor to the Forster's tern as a breeding bird in Illinois and other areas is the loss of nesting habitat. In Illinois this species seems dependent on larger lakes with marsh borders for nesting *02*. Developmental and recreational use of lakes and marshes may prevent the Forster's tern from nesting in Illinois *02*. In the Green Bay, Wisc. area this species is a regular nester in dense cattail and detrital cattail mat. 80% of this habitat was lost between 1966-1976 *04*. Another threat to terns has been the massive spraying of marshes with insecticides (mainly DDT) for mosquito control. Terres (1980) reports large numbers of terns, some 5 to 12 yrs. old, had been found dead on New England beaches; killed by DDT acquired from minnows *03*. Vandalism and intentional human disturbance still occur. Portnoy (1977) reported the abandonment of the largest Forster's tern colony (Grassy I) in Louisiana *21*. Natural enemies include: muskrat, mink, other gulls, foxes, racoons, weasels, rats *03,05*. Changing water levels destroys nests and eggs *SEE 23*.

Population parameters: No information is available on population size, relative trends, survival and mortality rates, sex ratio and average lifespan. This species has probably declined in Illinois with the loss of its preferred nesting habitat *02*. Bergman et al. (1970) reported 12% nesting success (N=107) *23*.

Comments on management practices:Apparently the Forster's tern in Illinois is dependent on larger inland lakes with marsh borders for nesting *02*. Developmental & recreational use of lakes and marshes may prevent this species from nesting in Illinois *02*. The Forster's tern has a sporadic history in the great lakes. In a known nesting area (Green Bay) 80% of its preferred habitat has been lost between 1966-1976 *03*. A latest threat to terns has been massive spraying of marshes with insecticides (mainly DDT) for mosquito control *03*. Human vandalism and disturbance is an extreme limiting factor. Intruders into colonies may crush young and eggs and in some areas of the country still shoot individuals *03,21*. Management in Illinois must include the maintainance of natural marsh conditions along borders of large inland lakes that provide potential nest habitat for the Forster's tern. Also, as with other marsh species, control of water quality may also play a critical role in maintaining breeding populations *02*. The Forster's tern is protected by the Illinois Endangered Species Act 1973 *02*, the Migratory Bird Treaty Act *19*, and the Illinois Wildlife Code, 1921 *21*.